Snake alpha-neurotoxins have been extremely useful ligands for identifying, localizing and purifying the nicotinic acetylcholine receptor found in vertebrate skeletal muscle and electric fish electric organs. These toxins have also been used to characterize a nicotinic binding site found in central and peripheral nervous tissue. By analogy with the skeletal muscle and electric organ studies, this nicotinic binding site has often been assumed to be the neuronal nicotinic acetycholine receptor. The major problem with this assumption is that in many neuronal systems, binding of alpha-neurotoxins to this binding site is not associated with a blockade of nicotinic transmission. However, in the chick ciliary ganglion several alpha-neurotoxins have been shown to block transmission in a manner consistent with binding to the physiological nicotinic receptor. The purpose of this study is to purify these alpha-neurotoxins using cation exchange chromatography and to characterize the binding of their radiolabelled derivatives to the chick ciliary ganglion. Filtration and centrifugation assays will be used to measure specific binding of toxins both to the known nicotinic receptor found in Torpedo electric organ and to chick ciliary ganglia homogenates and intact ganglia. Detergent - solubilized toxin-receptor complexes will be examined by sedimentation in sucrose gradient, polyacrylamide gel electrophoresis and isoelectric focusing, to determine whether one of several membrane proteins are involved in alpha-neurotoxin binding. It is hoped that these experiments will: 1) Identify and characterize the nicotinic acetylcholine receptor which is present in ciliary ganglia; 2) Clarify the role of alpha-neurotoxin binding sites in neuronal nicotinic transmission; 3) Provide a useful biochemical measure with which the development and regulation of nicotinic transmission in autonomic ganglia can be studied.